1. Field of the Invention
The present invention relates generally to optical fiber devices and related methods, and in particular to an improved dispersion-compensating system and a dispersion-compensating fiber with an improved figure of merit and effective area.
2. Background Art
Coherent detection followed by digital signal processing in the electrical domain is currently being investigated as an enabling technology for transmission systems with increased transmission rates. When both optical amplitude and phase are detected, linear impairments such as dispersion and polarization-mode dispersion (PMD) can be fully compensated in the electrical domain. This approach eliminates the need for optical dispersion compensation using dispersion-compensating fibers (DCFs), or like devices.
However, there are known disadvantages of an electrical domain approach to dispersion compensation. One disadvantage is that, when providing compensation for large amounts of dispersion, an electrical domain dispersion-compensating system requires large and expensive digital signal processing integrated circuits (DSPs), as well as high electrical power consumption. Thus, there exists a need for an improved approach for managing dispersion compensation in such systems.
Another issue is the “figure of merit” (FOM), a metric that is commonly used in the fiber optics industry to quantify the amount of loss added to an optical transmission system by a given fiber or fiber module. Generally speaking, the FOM for an optical fiber module is the ratio formed by dividing the numerical value of the dispersion of the optical fiber by the attenuation of that fiber at a particular wavelength. A high figure of merit signifies that a dispersion-compensating fiber module add less loss to the system.
Further, an optical transmission fiber with a large dispersion typically has a large effective area, Aeff. The effective area Aeff is inversely proportional to FOM. Thus, optical fibers with large effective areas tend to have low FOMs.
Thus, an ongoing challenge for fiber designers is the balancing of the effective area needed to achieve a given dispersion characteristic against the need for a sufficiently high FOM. Prior designs have provided fibers that display the following values for FOM and Aeff:
FOM=460 ps/(nm·dB); Aeff=21 μm2: M. Wandel et al., Proceedings of ECOC '2001, PD.A.1.4, and U.S. Pat. No. 6,490,398;
FOM=450 ps/(nm·dB); Aeff=17 μm2: M. Hirano et al., Proceedings of OFC/NFOEC '2009, OWN5; and
FOM=477 ps/(nm·dB); Aeff=70 μm2: S. Ramachandran, Journal of LightWave Technology, pp 3425, 2005.